1. Technical Field
This invention relates generally to a scanning device, and more specifically, to a scanning device incorporating a polygon scanning wheel and a magnification device for achieving both high speed and narrow field of view.
2. Discussion
In certain image acquisition systems, such as an integrated forward looking infrared (FLIR) laser radar imaging system, it is sometimes desirable to make a detailed scan of possible target locations in a larger imaged scene. Because these small target locations are generally a small portion of the overall scene, which may include a multitude of target locations, it is desirable to incorporate narrow or small angle field of view scanning having very fast scanning capabilities. An adequate combination of both high speed of scanning and small angle field of view has heretofore not been achievable in the prior art scanning systems.
As discussed above, it is necessary to achieve a reasonably high scan rate. Generally, it is required that a polygon-type scanner or an acoustooptic scanner be used to realize these scan speeds. For a polygon scanning wheel, the angular size of the scanned field of view is in an inverse relation to the number of facets the scanning wheel has. Therefore, in the prior art, a large number of facets were required for a narrow field of view. Further, a certain minimum number of incident beam diameters are required to impinge on a single facet to alleviate vignetting near the ends of the scan. As a result of at least these two conditions, for a scanning device having a very narrow field of view, the diameter of the scanning wheel will be unreasonably large. For the acoustooptic scanner, size constraints also become a problem, and further, optical transmission of the acoustooptic scanner is generally inadequate.
What is needed then is a polygon-type scanning wheel capable of achieving the desirable high scan rate, but which does not suffer from the size requirements of an appropriately numbered multi-faceted wheel of the prior art. It is therefore an object of the present invention to provide such a scanner.